1. Field of the Invention
The present disclosure relates generally to electrical circuits for system safety controls and, in particular, to emergency machine off system disabling circuits.
2. Description of the Related Art
A variety of equipment systems are utilized within the semiconductor fabrication industry, which include peripherals and ancillary components. From time to time, equipment systems require power down to facilitate safe service. A complicating factor arises when components and/or sub assemblies fail and/or require emergency service; thereby, impacting the entire system.
Industry safety standards require the use of an “emergency off circuit” (EMO) during any unplanned shutdowns and/or repairs activities. Activation of the EMO causes the entire system to halt/shutdown/power off. Therefore, some service personnel may attempt to override the EMO safety circuit to facilitate continued equipment operation during service procedures, fostering creating an unsafe condition. Various unsafe techniques are used. For example, service personnel can “jumper out” the systems EMO circuit rendering it inoperative, increasing the risk of employee injury during the service activity. Unfortunately, this technique does not control or protect personnel from all remaining hazardous energy sources within the system. Continuing operation in this manner may lead to significant personal injury, when for example, when toxic gas is delivered to a component that is not operational or involved with the primary maintenance activity.
What is needed are apparatus providing a safety control circuit design, such as the controls provided herein. When implemented, the apparatus provide safe controls for de-energizing/isolating selected equipment system components and sub-components, while other parts of the system remain active while ensuring all safety controls circuits remain fully functional for all aspects of the equipment system still in use.